Electrostatic recording utilizing tungsten-rhenium electrodes



Feb. 28, W67 J.J. MORGAN ELECTROSTATIC RECORDING UTILIZING TUNGSTEN-RHENIUM ELECTRODES Filed April 15, 1963 lantern-w.

PULSE 30 GENERATOR PULSE GENERATOR PULSE GENERATOR TUNGSTEN-RHENIUM PULSE GENERATOR INVENTOR. (/OHNC]. MORGAN 3 307,198 ELECTROSTATIC izEconDrNo UTILIZING TUNGSTEN-RHENIUM ELECTRODES John J. Morgan, Detroit, Mich., assiguor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed Apr. 15, 1963, Ser. No. 273,222 2 Claims. (Cl. 346-74) This invention relates to electrostatic recording or printing, and particularly'to the electrodes in electrostatic recording heads.

In electrostatic recording, an electrostatic charge is deposited ona record medium in accordance with the data, such as curves, alphanumeric information, or the like, to be recorded. In the usual system, the electrostatic charges are then developed by subjecting them to a powdered, dry ink which adheres to the charged areas but not to the uncharged areas, thereby making the charged areas .visible; and the developed charges are then fixed to the recording medium, as by heat and/or pressure.

The present invention is primarily directed to the electrodes for depositing the electrostatic charges.

In establishing the electrostatic discharges for depositing the charges onto the recording medium, the electrodes in the recording head are subjected to relatively high voltage pulses, in the order of 1500 volts.- These high voltage pulses tend rapidly to erode and to oxidize the electrodes, the effects of which cause the heads to act unreliably after a relatively short period of time. For example, in one application of an electrostatic recording system, the electrodes, made of stainless steel, were found to act unreliably after about ten hours of continuous operation, because of the eifects of erosion and oxidization. Other oxidation-resistant materials that had been used for the electrode were found to suffer the same short life properties. It is believed that the rapid oxidation and erosion of the electrode are primarily attributable to the ozone and heat generated in the electrical discharge field.

An object of the invention is to provide an electrostatic recording electrode system which exhibits a substantially lower degree of electrode erosion and oxidization when subjected to the high voltages frequently used in such systems.

A further object of the invention is to provide an electrostatic recording head which is capable of operating reliably over a much longer period than the previously used heads having electrodes made of stainless steel.

In accordance with a broad aspect of the invention, there is provided an electrostatic recording system having an electrode made of a conductive material comprising tungsten and rhenium. Preferably, the electrode is made of an alloy of tungsten and rhenium containing between 1030% rhenium.

For purposes of describing the present invention, there is illustrated an electrostatic recording head of generally similar construction as disclosed in Benn et al. US. Patent No. 3,068,479. The electrical circuit and the energization of the electrodes, however, are somewhat different from that patent. It is to be understood that the herein described embodiment is purely illustrative, and that the United States Patent M 3,307,198 Patented Feb. 28, 1967 trated in Benn et al. US. Patent 3,068,479;

' FIG. 2' is an enlarged perspective view, partially in section, of the salient elements of the electrostatic head in recording position with respect to the record medium;

FIG. 3 is a sectional view taken on line 3--3 of FIG. 2, the record medium and'its supporting anvil also'being shown in section for purposes of clarity;

FIG/'4 is a partial sectional view of'the electrostatic recording head of FIG. 1;

FIG. 5 is a similar partial sectional view but of a different embodiment of the invention;

FIG.'6 is a bottom plan view of another form ofelectrostatic recording head particularly useful for printing alphanumeric information. i

The electrostatic recording head of FIG. -1, generally designated 10, is formed of two integrated parts, a recording face portion 11 and a connector-carrying portion 12. The former portion carries a plurality of equally-spaced pin electrodes 14 and a bar electrode 16 molded into a body of insulating material 18. Each pin elecrtode 14 is connected to a resistor 22 embedded in the insulating body 18. A connector 20 is provide for each pin electrode 14, the connector being connected to its respective electrode 14 and its respective resistor 22 by a lead 23. Bar electrode 16 is connected to a connector 21 through the lead 22'. All the pin electrodes 14 are arranged in a line on the front face, or recording face, of the recording head 10, and are all equally spaced from each other and from the bar electrode 16. The recording face of the head is flat and all the electrodes terminate substantially flush with and are exposed on that face. The opopsite face of the recording head, which is in the connector-carrying'portion 12, carries the connectors 20 and 21 also arranged in a line. i I

In operation, the recording head 10 is-disposedover a conductive anvil 24, and the record medium 28 is passed bet-ween the recording head and the anvil. The record medium may be made of paper or other material adapted to retain an electrostatic charge when one is deposited by the electrodes of the recording head. The charges are deposited on the record medium 28 'by applying voltage pulses to selected pins 14, which causes an electrical discharge between the pulsed pins 14 and the common bar electrode 16.

The structure of the recording head is more clearly seen in FIGS. 3 and 4. In producing the recording face portion 11 of the head, a thin sheet of mica is fused to the bar electrode 16, the pin electrodes 14 are then placed on top of the mica 30, and an insulating material, such as mica-filled epoxy resin containing about two parts by weight of mica to one part by weight of epoxy resin, is applied to encapsulate the pin electrodes 14, the bar electrode 16, and the separating mica layer 30. The pin 3 be the same mica-filled epoxy resin used to bond together the electrodes at the recording face of the head.

In the illustrated head, the pin electrodes 14 are wires of approximately .005 inch in diameter and the bar electrode 16 is of a conductive material of about the same thickness as the diameter of the pin electrodes 14, but the bar electrode may be substantially thicker since its thickness is not critical. Mica layer 30 is approximately .001 inch in thickness, spacing the 'bar electrode 16 from all the pin electrodes 14 by .001 inch. The spacing between the pin electrodes 14 is approximately .047 inch. Inter- .pin spacing must be greater than pin-to-bar spacing so as to preclude pin-to-pin arcing.

The electrostatic recording head illustrated may be used in a circuit schematically shown in FIG. 2. Each pin electrode 14 is connected to its resistor 22 and to a pulsing circuit comprising a pulse generator 30' and a pulse transformer having a primary winding 32 coupled to the pulse generator and a secondary winding 34 connected to its pin electrode through its resistor 22. The other'side of the secondary winding 32 is connected to the bar electrode 1 6. In operation, pulse generator 30 generates a pulse in secondary winding 34 of approxi mately 1500 volts negative which is applied between its respective pin electrode and the bar electrode 16. The pin, being driven negative, acts as a cathode, and the bar acts as an anode. This pulse is sufiicient to cause an electrostatic discharge between the two electrodes, which produces an electrostatic charge on record medium 28. Resistor 22 is of high impedance and functions to limit the current when an electrical discharge is produced. It has a value of 470,000 ohms in a typical circuit. Anvil 24, which may also be considered as an electrode since it is made of conductive material, is grounded in the circuit illustrated.

It is thus seen that by applying negative pulses between preselected pin electrodes 14 and their common bar electrode 16, one may deposit electrostatic charges on the record medium 28 in accordance with the pins pulsed.

As briefly mentioned earlier, the pin electrodes 14 and the bar electrodes 16 in this type of head had previously been made ofstainless steel, and probably other materials that had relatively high oxidation-resistant properties under normal environmental conditions. Nevertheless, it was still found that such heads had a relatively short li-fein certain applications involving continuous and high frequency operation, because of the effects of oxidization and erosion on the pin electrodes 14 produced by the very severe operating conditions.

In the present invention, the pin electrodes 14 are made of a conductive material comprising tungsten and rhenium. It was found that when this material was used for the pin electrodes 14, the life of the recording head was remarkably extended. For example, in one application where 1500 volts were applied between the pin and bar electrodes at a frequency of 700 cycles per second, the previously-used head having cathode pins and an anode bar of stainless steel began to act unreliably after about ten hours of continuous operation. Inspection showed that this unreliable operation was caused by oxidation and erosion at the stainless steel cathode pins. In sharp contrast to this relatively short life, a head utilizing cathode pins of the tungsten-rhenium material operated continuously for over 300 hours under the same conditions as the stainless steel heads. It was found that the tungstenrhenium alloy pin electrodes exhibited very little erosion and oxidization effects even after that long period of operation, and therefore, in all probability, it could have operated many more hundreds of hours.

Preferred tungsten-rhenium materials for making the pin electrodes 14 are tungsten-rhenium alloys having between 20-30% rhenium. In the head tested an alloy of 74% tungsten and 26%rhenium was used.

The material for bar electrode 16 does not appear to be as critical. A preferred material is tantalloy, which 4 is an alloy of tantalum and 10% tungsten. Very good results have also been obtained by usingsubstantially pure tungsten for bar electrode 16. The same tungsten-rhenium alloy used for the pin electrodes could also be used for the bar electrode.

FIG. 5 illustrates a variation of the electrostatic printing head. In this variation, the pin electrodes 14 are arranged between a pair of bar electrodes 16 and 16', each bar electrode having bonded thereto a thin layer of mica 30 and 30' to insulate the pin electrodes from the two bar electrodes. The structure of the head is otherwise the same as described above, and the head may be used in the same type of circuit as illustrated in FIG. 2, whereupon the two bar electrodes 16 and 16' would be electrically connected together.

FIG. 6 illustrates a further variation of an electrostatic printing head constructed in accordance with the invention. This variation, generally designated 110, is particularly useful for recording alphanumeric information, and is similar in structure to that illustrated in FIG. 6 of the Benn et al. U.S. Patent No. 3,068,479, as well as that disclosed in Howell U.S. Patent No. 2,918,580. This is a matrix-type head and includes 5 assemblies of the pin and bar electrodes described above in one head. That is, there are 5 bar electrodes 116 and a plurality (in this case 7) pin electrodes 114 for each bar electrode, or a total of 35 pin electrodes. Pin electrodes 114 are comparable to and may be made of the same material as pin electrodes 14 in the above-described embodiments, and bar electrodes 116 are comparable to and may be made of the same material as bar electrode 16. Each would also include the .001 inch mica spacer between each bar electrode and its group of pin electrodes. This head is particularly useful in a system for printing alphanumerical information using coincident pulses. By applying coincident pulses to selected pin electrodes 114 and selected bar electrodes 116, electrostatic charges are deposited on the record member in accordance with the desired character to be printed. Further information as to this type head and its application is available in the above-referenced patents.

It is understood that the present invention is not limited to the electrostatic heads illustrated, but maybe used in other electrostatic heads and in other systems. For example, it could be used in heads having cathode electrodes shaped in accordance with the alphabetical or numerical characters to be printed, instead of the pin electrodes illustrated. Many other variations, modifications and applications of the invention will be apparent to those skilled in the art coming within the spirit and scope of the invention as defined in the following claims.

I claim:

1. In an electrostatic recording head including an anode bar electrode and a plurality of cathode pin electrodes positioned closely to said anode electrode but electrically insulated therefrom, and further including a surrounding body of electrically insulating material encapsulating the electrodes therewithin except for the exposure of the terminal ends thereof across which a relatively high voltage is established by the selective application of negative electrical pulses to the cathode pin electrodes, the provision for inhibiting erosion of the pin electrodes which comprises forming the same of an alloy of tungsten and rhenium of which the rhenium constitutes substantially 20%-30% of the alloy.

2. In an electrostatic recording head including a cathode electrode and an anode electrode closely disposed but electrically insulated from one another and in operation receiving a relatively high voltage across the same in the form of negative pulses applied to the cathode electrode, the improvement characterized in that the cathode electrode is composed of an alloy of tungsten and rhenium wherein the rhenium is within the range of substantially 20%30% of the alloy.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Lohmann 75176 Hensel 75176 Cobine 75176 Erving 346139 Nelson 346745 6 FOREIGN PATENTS 7/1959 Great Britain.

OTHER REFERENCES BERNARD KONICK, Primary Examiner.

Howell 34674 X 10 I, BREIMAYER, Assistant Examiner. 

1. IN AN ELECTROSTATIC RECORDING HEAD INCLUDING AN ANODE BAR ELECTRODE AND A PLURALITY OF CATHODE PIN ELECTRODES POSITIONED CLOSELY TO SAID ANODE ELECTRODE BUT ELECTRICALLY INSULATED THEREFROM, AND FURTHER INCLUDING A SURROUNDING BODY OF ELECTRICALLY INSULATING MATERIAL ENCAPSULATING THE ELECTRODES THEREWITHIN EXCEPT FOR THE EXPOSURE OF THE TERMINAL ENDS THEREOF ACROSS WHICH A RELATIVELY HIGH VOLTAGE IS ESTABLISHED BY THE SELECTIVE APPLICATION OF NEGA- 